Suddenly, another sound smote his ear, that as of a diver rising to the surface; then came a hard breathing on the water, and the regulated plashing as of some one swimming away into that very obscurity which the earl's eyes ached with regarding, but failed to penetrate. His hair bristled, and his heart quailed with momentary terror of a spirit, or evil thing; but from that very terror he gathered a courage, and, by his oar and hands, feeling the rocks on each side, shot further in his sharp-prowed boat, intent on overtaking the swimmer, and discovering whether it was a man or devil; but he had not gone twenty yards when the chasm terminated in a sheer wall of rock; and again he paused to listen. The dash of the water had ceased.
He thought he heard other sounds, like those of footsteps clambering up the rock; but feared he was mistaken, for all became immediately still, and he heard only the murmur of the water as it boiled among the reefs without.
"Tush!" thought he, reddening with shame at his own alarm; "it has only been some poor seal or sea-dog basking on the rocks in the summer moonlight. By midnight the moon will be in the west—till then let me sleep, for these last two nights I have never closed an eye;" and looping a rope round a pinnacle of rock, he securely moored the boat, and reclined within it to sleep.
Such was the effect of the weariness oppressing him, that in three minutes he was buried in profound slumber, rocked by the motion of the boat, which gently rose and fell on the undulations of the water; for though around the isle the swell was heavy, the waves being broken by the jutting of the rocks at the cavern mouth, they rolled gently and smoothly into its dark recesses.
Now while the earl all unconsciously was sleeping, this little cavern of the sea was filling fast; for as the rising tide on the German Ocean met the downward current of the Forth, the water rose rapidly against the impending walls.
Ashkirk knew not how long he slept, when he was suddenly awakened by an unusual sound, and, on attempting to rise, struck his head with violence against the stone roof of the cave, close up to which his boat had floated on the rising tide.
His situation was fraught with danger and horror.
Moored fast to a point of rock now far beyond his reach, the boat was wedged between the top of the cavern and the surface of the swollen water, leaving him thus imprisoned, coffined, as it were, in utter darkness, and with the deadly fear that the whole of this now submarine grot would be covered by the gurgling tide, in which case he would assuredly be drowned, "and die the death (as he thought) of a rat in a drain."
The partial gleam of moonlight which had illuminated the mouth of this frightful trap had now passed away, and the darkness within and around it seemed palpable and opaque. He could no longer discern where the entrance lay, and his heart sank in the fear that the water had risen over it. He now heard the wavelets rippling, with a thousand hollow echoes, in the fissures and recesses, and gurgling with a sucking sound as they filled each in succession, and rose towards the gunwale of his boat, which had become perfectly immovable.
And the tide was still rising!